| Summary: | 碩士 === 國立臺灣大學 === 臨床牙醫學研究所 === 100 === The past researchers only put emphasis on comparisons of ultrasonic cutting abilities among the commercial products. Due to difficulties in experimental designs, less attention was paid to effects of different frequencies and amplitudes on cutting dental tissues. Selective cutting ability of ultrasound is beneficial to oral and maxillofacial surgery or other dental treatments. Protection of surrounding soft tissues could be obtained, but caries removal with ultrasonic energy is difficult. We usually treat dental caries with rotary instruments. Accidental pulp exposure may occur if we use the instruments improperly. As excessive tissue was removed, unfavorable influences on the preservation of pulp vitality could happen.To investigate the impacts of ultrasonic energy on dentin cutting, caries removal and pulp damage, the following methods were used: (1) To measure the amplitudes of 32kHz, 40kHz, 56kHz and 66kHz along X-axis, Y-axis and Z-axis with fibro-optic interferometer. (2) To establish a standardized ultrasound-dentin cutting test model with instron and to compare cutting efficiencies of dentin and demineralized dentin of different frequencies. (3) To set up a reliable experimental animal model and use a histological scoring system to evaluate effects of air-driven high-speed dental handpiece and ultrasonic device on dental pulp tissues.As the ultrasonic frequency increased, the amplitude along the Y-axis became smaller. The amplitudes along the X-axis and Z-axis showed little difference among each group. Dentin cutting efficiency of 32kHz was the best while efficiency of 56kHz was the worst. The best frequency to remove demineralized dentin was 40kHz, but there was no statistically significant difference between 40kHz and 56kHz as well as 56kHz and 66kHz. Higher score of immediate pulp reaction obtained from High-speed group indicated that more pulp damage was caused by the air-driven high-speed dental handpiece. Higher score of long-term pulp response obtained from Ultrasonic group revealed that ultrasonic cutting was more favorable for preservation of pulp vitality.Recently, frequency provided by commercial ultrasonic devices is around 30kHz. It is also shown in our study that the frequency is the most suitable for cutting dental hard tissue or bone. In our study, dentin cutting efficiency of 66kHz was also good and it could cut soft tissue. The frequency of 66Hz seemed worthy of further investigation. On the other hand, ultrasonic devices do less harm to the dental pulp tissue, and it may become a potential instrument for replacement of rotary instruments to treat deep caries and prevent from excessive pulp damage.
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